.nav{
    height: 100px;
    background-color: var(--colors_1);
    width: 100%;
    min-width: 375px;
}
.nav_logo{
    width: 200px;
    height: 44px;
    object-fit: contain;
}
.nav_container{
    display: flex;
    justify-content: space-between;
}
.nav_links{
    display: flex;
    width: 700px;
    justify-content: space-around;
    align-items: center;
    margin-block-start: 0;
    margin-block-end: 0;
}
.nav_links a{
    color: var(--colors_2);
    text-decoration: none;
}
.nav_links a.nav_active,.nav_links a:hover{
    color: white;
}
.nav_hamburg{
    display: none;
}
.nav_hamburg span{
    width: 25px;
    height: 2px;
    display: block;
    margin: 7px;
    opacity: 1;
    transition: 0.3s;
    background-color: white;
}
.nav_hamburg_active span:nth-child(2){
    opacity: 0;
}
.nav_hamburg_active span:last-child{
    margin-top: -9px;
    transform: rotate(-45deg);
}
.nav_hamburg_active span:first-child{
    margin-bottom: -9px;
    margin-top: 13px;
    transform: rotate(45deg);
}
.nav_mask{
    width: 100%;
    position: fixed;
    top: 0px;
    background-color: var(--colors_1);
    opacity: 0.5;
    z-index: 8;
}
@media (max-width:768px){
    .nav{
        height: fit-content;
        min-height: 100px;
        position: relative;
        z-index: 10;
    }
    .nav_container{
        flex-wrap: wrap;
        margin-top: 25px;
    }
    .nav_links{
        width: 100%;
        display: none;
        margin-top: 20px;
        flex-wrap: wrap;
    }
    .nav_links li{
        width: 100%;
    }
    .nav_links li a{
        display: block;
        width: 100%;
        height: 40px;
        text-align: center;
    }
    .nav_hamburg{
        display: block;
        padding-top: 5px;
    }
    #nav{
        position: absolute;
    }
    /*由于导航栏使用了绝对定位，在768下banner会被导航栏遮挡，
    所以把banner设为相对定位，这不会影响index.html，
    只对div.page_banner有效*/
    .nav_mask+div.page_banner{
        position: relative;
        top: 100px;
        margin-bottom: 100px;
    }
}